Frames .. glass sills....
same brush...
surely you dont change your brush simply to wipe the sill?...
i asked this question about spotting a year ago...
first cleans... dirt under the seal..
but most of the time its a broken seal,... you can normally see it after a rinse... one line of water still there as you move to the next window....
with them, i always clean it , rinse it and at the very end ... i go back to it and rinse from the top again.. without actually touching any part of the frame/seal...
but more often than not its a lack of proper rinsing... i have learnt my lesson not to be tight with the pure water.
